Hypercapnia augments resistive exercise‐induced elevations in intraocular pressure in older individuals

Mekjavic, Igor B.; Amoaku, Winfried; Mlinar, Tinkara; Mekjavic, Polona Jaki

Abstract

The present study assessed the effect of 6° head down (establishing the cephalad displacement noted in astronauts in microgravity) prone (simulating the effect on the eye) tilt during rest and exercise (simulating exercise performed by astronauts to mitigate the sarcopenia induced by unloading of weight‐bearing limbs), in normocapnic and hypercapnic conditions (the latter simulating conditions on the International Space Station) on IOP.

Volunteers (average age = 57.8 ± 6 yrs.; N = 10) participated in two experimental sessions, each comprising: i) 10‐min rest, ii) 3‐min handgrip dynamometry (30% max), and iii) 2‐min recovery, inspiring either room air (NCAP), or a hypercapnic mixture (1% CO2, HCAP). We measured IOP in the right eye, cardiac output (CO), stroke volume (SV), heart rate (HR) and mean arterial pressure (MAP) at regular intervals.

Baseline IOP in the upright seated position while breathing room air was 14.1 ± 2.9 mmHg. Prone 6° HDT significantly (p < 0.01) elevated IOP in all three phases of the NCAP (rest: 27.9 ± 3.7 mmHg; exercise: 32.3 ± 4.9 mmHg; recovery: 29.1 ± 5.8 mmHg) and HCAP (rest: 27.3 ± 4.3 mmHg; exercise: 34.2 ± 6.0 mmHg; recovery: 29.1) trials, with hypercapnia augmenting the exercise‐induced elevation in IOP (p < 0.01). CO, SV, HR and MAP were significantly increased during handgrip dynamometry, but there was no effect of hypercapnia.

The observed IOP measured during prone 6°HDT in all phases of the NCAP and HCAP trials exceeded the threshold pressure defining ocular hypertension. The exercise‐induced increase in IOP is exacerbated by hypercapnia.

Citation

Mekjavic, I. B., Amoaku, W., Mlinar, T., & Mekjavic, P. J. (2020). Hypercapnia augments resistive exercise‐induced elevations in intraocular pressure in older individuals. Experimental Physiology, 105(4), 641-651. https://doi.org/10.1113/ep088236

• Journal Article Type: Article
• Acceptance Date: Feb 7, 2020
• Online Publication Date: Feb 8, 2020
• Publication Date: Apr 1, 2020
• Deposit Date: Mar 2, 2020
• Publicly Available Date: Feb 9, 2021
• Journal: Experimental Physiology
• Print ISSN: 0958-0670
• Electronic ISSN: 1469-445X
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 105
• Issue: 4
• Pages: 641-651
• DOI: https://doi.org/10.1113/ep088236
• Keywords: Physiology
• Public URL: https://nottingham-repository.worktribe.com/output/4077589
• Publisher URL: https://physoc.onlinelibrary.wiley.com/doi/abs/10.1113/EP088236
• Additional Information: This is the peer reviewed version of the following article: Mekjavic, I.B., Amoaku, W., Mlinar, T. and Mekjavic, P.J. (2020), Hypercapnia augments resistive exercise‐induced elevations in intraocular pressure in older individuals. Exp Physiol. Accepted Author Manuscript, which has been published in final form at https://doi.org/10.1113/EP088236. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.